Total synthesis of amphilectane-type diterpenoids: (±)-8,15-diisocyano-11(20)-amphilectene

A total synthesis of the structurally novel, antimicrobial diterpenoid (±)-8,15-diisocyano-11(20)-amphilectene (2) is described. Alkylation of 2-methoxycarbonyl-3-methylcyclohexanone (13) with (E)-1-(tert-butyldimethylsiloxy)-6-iodo-3-(trimethylstannyl)-2-hexene (14) provided, stereoselectively, the functionalized keto ester 15, which was converted efficiently into the diene 17. Diels–Alder reaction of 17 with acrolein, followed by base-catalyzed equilibration of the resultant product mixture, gave the aldehydes 19 (58%) and 20 (29%). Allylic oxidation of the alkene 24 (derived from 19) afforded the enone 25. Reduction (Na, NH 3 , t-BuOH) of 25 gave 28, which was converted, via a sequence of eight synthetic steps, into the diacid 45. Efficient transformation of the carboxyl functions of 45 into isonitrile groups completed the synthesis of (±)-2.